At the current time the existence of numerous thermoplastic products that employ starch in their composition is widely known. Thus, for example, patents EP0947559B1 and EP0950689 describe biodegradable compositions based on thermoplastic starch and a thermoplastic polymer that is incompatible with starch, with good resistance to humidity or to impacts in which the starch constitutes the dispersed phase and the thermoplastic polymer constitutes the continuous phase, but they do not consider mixtures with natural or synthetic latex polymers in aqueous dispersion, nor with starch in co-continuous or continuous phase, nor the advantages that these may represent.
Patents EP0937120B1, EP1526156, EP2270093, EP0965615A1 and EP0950690B1, as in the previous patents, also describe biodegradable compositions based on thermoplastic starch and a thermoplastic polymer incompatible with the starch, in which the starch constitutes the dispersed phase and the thermoplastic polymer constitutes the continuous phase, and they also require an interfacial agent such as polyhydric alcohol esters, non-ionic water-soluble surfactants or products of the reaction of diisocyanates with polymers with terminal groups capable of reacting with isocyanates. Neither do these patents contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in co-continuous or continuous phase, nor the advantages that these can provide.
Also known are certain patents such as WO037749A2, which use a procedure based solely on the size of the particles to guarantee the mixture. However, they do not contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in co-continuous or continuous phase, nor the advantages that these can provide compared to the complexity of having to control the size of the particle in the mixture.
Furthermore there are patents U.S. Pat. No. 0,182,196A1 and U.S. Pat. No. 7,241,832B2, which describe mixtures of thermoplastic biodegradable polymers with enhanced properties compared to their constituent polymers. In particular, mixtures of biodegradable thermoplastic polymers such as ECOFLEX, BIOMAX AND PLA with thermoplastic starch. However, they do not contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in co-continuous or continuous phase, nor the advantages that these can provide.
Moreover, in the examples of US2005/0182196, the maximum thermoplastic starch content is 50%, while in our invention it amounts to 57% thanks to the presence of latex.
On the other hand there are patents U.S. Pat. No. 0,039,303A1, U.S. Pat. No. 6,472,497B2 and U.S. Pat. No. 6,235,815B1 that describe the use of biodegradable thermoplastic polymers as starch plasticizers, allowing thermoplastic starch to be obtained without the need to use low molecular weight plasticizers such as glycerine.
However, they do not contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in the co-continuous or continuous phase, nor the advantages that these can provide.
Moreover, in the examples of U.S. Pat. No. 0,039,303A1, U.S. Pat. No. 6,472,497B2 and U.S. Pat. No. 6,235,815B1, the maximum thermoplastic starch content is 52.5%, while in our invention it amounts to 57% thanks to the presence of latex.
There also exists U.S. Pat. No. 6,962,950B1 that describes mixtures of a hydrophobic polymer matrix, incompatible with starch, with a starch complex and a coupling agent that has groups that are compatible with the starch complex and with the hydrophobic polymer.
It needs to use, as the complexing agent, polylactic acid, polyglycolic acid, poly (lactic-glycolic) acid copolymers, ethylene-acrylic acid copolymers, ethylene-vinylacetate copolymers as well as copolymers of ethylene with polar monomers.
It cites, as the coupling agent, vinyl silanes, alkyl titanate and bis-3-triethoxysilylpropyl tetrasulphide.
It does not contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in co-continuous or continuous phase, nor the advantages that these can provide. Neither does it give any information on the properties of the films that are achieved.
Furthermore, it mentions that the maximum content of starch complex dispersed in the hydrophobic polymer matrix is 50%, while in our invention we achieve up to 57% thermoplastic starch thanks to the presence of latex.
Also known are patents ES2380274 T3 and U.S. Pat. No. 0,305,240A1 that describe a polymeric material containing starch or a starch derivative, polyester and a polymer that contains epoxide groups, especially recommended are copolymers that contain glycidyl methacrylate. In this polymeric material the starch is in the dispersed phase and the polyester is in the continuous phase. The epoxide groups create an intramolecular and intermolecular chemical association of starch and polyester which enhances the mechanical properties of films, allowing the thermoplastic starch content to be increased from 33% to 40% (7%), while maintaining suitable mechanical properties.
It does not contemplate mixtures with polymers in aqueous dispersion, of the natural or synthetic latex type, nor with starch in co-continuous or continuous phase. In our invention the addition of latex makes it possible to increase the thermoplastic starch content to up to 57%, obtaining films with suitable properties for applications such as bags, wrappings for healthcare products, films and products for agriculture, injected parts, moulded parts . . . .